The present invention relates to a stent used to ensure a desired inner diameter of a tubular organ or bodily lumen, and in particular, to a method for delivering and recovering the stent.
Stents are often employed to maintain the internal diameter of a bodily lumen, and in particular, to maintain the expanded internal diameter of a bodily lumen that has been expanded by a related medical procedure. For example, in an angioplasty procedure, a narrowed portion of the coronary arteries may be expanded with an angioplasty catheter. It is then typically necessary to take measures to prevent the expanded portion from being narrowed again. In such a case, an expansion retainer, hereinafter referred to as “stent,” is generally used for for ensuring a desired inner diameter of a bodily lumen. For ensuring expansion of, for example, a blood vessel by using a stent formed of stainless steel, the stent may be introduced into a predetermined position of the blood vessel through an angioplasty catheter. In the case of a balloon-expandable stent, a balloon disposed at the distal end portion of the catheter may then be expanded so as to expand the stent to a diameter conforming to the desired inner diameter of the blood vessel. Other types of stents are self-expanding and automatically expand to engage the vessel wall upon release from a delivery catheter.
Once expanded, a typical stent cannot be moved unless an external force is applied to the stent. Thus, it may be quite difficult to remove a stent left in the blood vessel, even after recovery of the body part to which the surgical operation was applied. In addition, it can be very difficult to change the position of the stent once it has been deployed and expanded. This may be problematic if the stent has been placed in an erroneous position or location during the initial deployment.
In some instances, stents used in the gastrointestinal system are constructed of plastic, allowing them to be retrieved and/or replaced during a follow-up procedure. However, plastic stents have two disadvantages. First, plastic stents are typically not expandable. In other words, plastic stents cannot be expanded like the self-expanding or balloon-expandable stents described above. Second, the diameter of a plastic stent is limited by the delivery system, typically a catheter, especially if delivered through an endoscope (˜11.5 French maximum). Due to the limited diameter of endoscopically delivered plastic stents, these stents are often prone to clogging (e.g., stents deployed in the bile or pancreatic duct) and may have to be replaced every three months, or even more frequently.
In other instances, larger diameter self-expanding stents have been delivered in vivo and deployed in the gastrointestinal system. Because of their larger expanded diameter, such metal stents remain patent longer than plastic stents, averaging perhaps 6 months before clogging. These types of stents are based on a self-expanding metal skeleton typically constructed of a metal alloy such as stainless steel or nitinol. In order for the larger diameter stents to collapse into delivery systems, various mesh or wire geometries are employed. However, the wire and mesh geometries allow for tissue in-growth, rendering the stent essentially “permanent.” When the stent becomes occluded, an additional stent (metal or plastic) can be deployed through the inner lumen of the clogged stent. Accordingly, these types of self-expanding stents are typically only utilized for the palliation of malignancies.
Therefore, a need exists for an expandable stent that can be efficiently and safely removed after some weeks or months in the body, thereby allowing the deployment of the stent in benign situations.